The field of the invention relates to coalescing media, coalescing systems, and methods for coalescing a mixture of two phases, namely a continuous phase and a dispersed phase. In particular, the field relates to coalescing media, coalescing systems, and methods for coalescing drops of the dispersed phase in order to collect and remove the dispersed phase from the mixture.
Coalescers are used widely to remove immiscible droplets from a gaseous or liquid continuous phase, such as in crankcase ventilation filtration, fuel water separation, and oil-water separation. Prior art coalescer designs incorporate the principles of enhanced droplet capture and coalescence by utilizing graded capture (i.e., decreasing fiber diameter, pore size and/or porosity in coalescing media) or by utilizing thick depth coalescers. Often, prior art coalescing media may have a more open layer upstream of an interior layer in order to increase life of the coalescer or downstream of an interior layer to increase the size of released drops. Wettability also is recognized as affecting coalescer performance. (See, e.g. U.S. Pat. No. 6,767,459 and U.S published Patent Application Nos. 2007-0131235 and 2007-0062887). U.S. Pat. No. 5,443,724 discloses that the media should have a surface energy greater than water in order to improve coalescer performance (i.e., that the media should be preferentially wetted by both coalescing droplets and continuous phases). U.S. Pat. No. 4,081,373 discloses that coalescing media should be hydrophobic in order to remove water from fuel. U.S. published Patent Application No. 2006-0242933 discloses an oil-mist coalescer in which the filtration media is oleophobic, thereby enabling the fluid mist to coalesce into droplets and drain from the filtration media. This published application also discloses that a second media layer optionally may be hydrophobic.
With regard to the removal of water from fuel, there is a need to increase removal efficiency and to remove smaller droplets than in the past, in order to protect high pressure rail fuel-injection systems. This challenge is further magnified by the introduction of new fuels, including ultra-low sulfur diesel (ULSD) and biodiesels with lower interfacial tensions and different additive packages, than fuels in the past. In fuels with lower interfacial tension, the size of dispersed drops is decreased, making the drops more difficult to remove. Enhanced coalescence therefore is needed to meet these challenges. Improved coalescers that include improved coalescing media also are desirable because they permit the use of a smaller media pack in view of improved coalescing efficiency. In fuels with lower interfacial tension, the size of drops is decreased, making the drops more difficult to remove. Enhanced coalescence therefore is needed to meet these challenges. Improved coalescers that include improved coalescing media also are desirable because they permit the use of a smaller media pack in view of improved coalescing efficiency.